1. Field of the Invention
The present invention relates to a method for double patterning a thin film on a substrate, and more particularly to a method for double patterning a thin film on a substrate by partially transferring a double pattern to an anti-reflective coating (ARC) layer overlying the thin film.
2. Description of Related Art
In material processing methodologies, pattern etching comprises the application of a thin layer of light-sensitive material, such as photo-resist, to an upper surface of a substrate that is subsequently patterned in order to provide a mask for transferring this pattern to the underlying thin film on a substrate during etching. The patterning of the light-sensitive material generally involves exposure by a radiation source through a reticle (and associated optics) of the light-sensitive material using, for example, a photo-lithography system, followed by the removal of the irradiated regions of the light-sensitive material (as in the case of positive photoresist), or non-irradiated regions (as in the case of negative resist) using a developing solvent. Moreover, this mask layer may comprise multiple sub-layers.
More recently, a double patterning approach has been introduced to allow the patterning of smaller features at a smaller pitch than what is currently possible with standard lithographic techniques. One approach to reduce the feature size is to use standard lithographic pattern and etch techniques on the same substrate twice, thereby forming larger patterns spaced closely together to achieve a smaller feature size than would be possible by single exposure. During double patterning, the substrate is exposed to a first pattern, the first pattern is developed in the light-sensitive material, the first pattern formed in the light-sensitive material is transferred to an underlying layer using an etching process, and then this series of steps is repeated for a second pattern.
Additionally, once the pattern is transferred to the underlying thin film, it is essential to remove the mask layer while not damaging the material properties of the underlying thin film. For example, the thin film may comprise a low dielectric constant (low-k, or ultra-low-k) dielectric film that may be used in back-end-of-line (BEOL) metallization schemes for electronic devices. Such materials, which may include non-porous low-k dielectrics as well as porous low-k dielectrics, are susceptible to damage, e.g., degradation of dielectric constant, water absorption, residue formation, etc., when exposed to the chemistries necessary for removal of the mask layer and its sub-layers. Therefore, it is important to establish pattern transfer schemes that reduce the potential for damaging the underlying thin film when forming such a pattern and removing the necessary mask layer(s).